The present invention generally relates to internal combustion engines. In particular, the present invention relates to light weight internal combustion engines which can be run on multiple different types of fuels including gasoline and alcohol based fuels and heavy fuels such as diesel fuel, JP5, JP8, Jet-A and kerosene based fuels.
Internal combustion engines are run on a variety of different types of fuels including gasoline, alcohol based fuels and heavy fuels such as diesel fuel, JP5, JP8, Jet-A and kerosene. Typically, gasoline powered or fueled engines operate at compression ratios of approximately 10 to 1 to as low as 5 to 1 whereas diesel and other heavy fuel engines generally require much higher compression ratios, typically on the order of 17 or 20 to 1. This difference in compression ratios is due to the different types of ignition systems used for gasoline engines versus heavy fuel engines.
For example, gasoline, which has a relatively low boiling point of approximately 135xc2x0 F. at sea level, readily forms vapors in air at atmospheric pressure, such that gasoline fueled engines typically can be spark ignited and operate with a stoichiometric air-fuel ratio. Heavy fuels, by contrast, have higher boiling points, i.e., approximately 350xc2x0 F. at sea level for diesel fuel, and therefore heavy fuels such as diesel fuel do not readily form such vapors under ambient conditions, making ignition of heavy fuels with spark ignition systems difficult. Thus, heavy fuels generally are used in compression ignition engines in which the fuels are injected under very-high pressures or compression loads to generate sufficiently high heats of compression in the engine cylinder to raise the temperature of the air in the engine cylinder above the ignition point of the heavy fuel. The fuel is then vaporized and burned in the heated air in the cylinder to drive the engine. The HIGH boiling point of heavy fuels makes them less volatile so that these fuels do not readily form vapors at ambient temperatures, making such fuels impractical for use in typical spark ignition engines. For example fuels like kerosene are sometimes used in spark ignition engines, but only after the engine is started with gasoline and operated to raise the engine temperature to a point where vaporization of the kerosene fuel can occur.
The high compression loads resulting from the combustion of heavy fuels also places significant strain on the engine components, requiring such engine components to be formed from thicker, heavier materials to withstand these high compression loads. Since gasoline does not require high compression ratios, with their resultant high compression loads, gasoline engines typically can be lighter, smaller and more portable than heavy fuel engines that produce comparable horsepower but which require significantly heavier, larger engine components in order to be able to withstand the high compression ratios generally required to ignite heavy fuels.
As a result, most heavy fuel powered applications are limited to large, heavy compression engines such as are found in large vehicles such as trucks. Gasoline engines, which can be smaller and lighter in weight, generally are used for smaller applications such as generators and fans or blowers or similar applications for ease of portability and use. For example, the military uses a number of different types of small, light weight gasoline powered engines for use as generators, fans and blowers, pumps, including pumps for fire suppression systems, and other applications such as M17 portable decontamination units for use in the field. Heretofore, diesel or other heavy fuel powered engines have been impractical for use in such applications in the field where portability and ease of storage are necessary, due to the larger sizes and significant weight of such heavy fuel engines.
The problem with gasoline powered engines is, however, that the ability of gasoline to readily form vapors in ambient air at low atmospheric pressure, which enables easy ignition, makes gasoline extremely volatile and dangerous to handle and use as a stray spark and even excessive heat can ignite the gasoline vapors. In addition, in many applications in fields such as construction or military operations, diesel fuel or other heavy fuels are readily available and are used for vehicles such as heavy trucks, bulldozers and the like, whereas gasoline must be brought to the site in containers and stored as a hazardous material.
For example, on Navy ships the engines and most heavy pump or turbine systems are driven using diesel fuel and typically the only use for gasoline on these ships is for the pumps for fire suppression systems, which are required to be light weight and small in size so that they can readily be carried through doors and to various locations throughout the ship. The gasoline is, however, among the most dangerous and volatile materials on the ship. In addition, the military has indicated a desire to standardize the fuel used for all applications, with its preference to being a use of lower cost, safer to handle and use heavy fuel such as JP8 or diesel and to avoid the use of different types of fuels for different applications, especially the use of gasoline due to its volatility and handling requirements for use in the field. It is still necessary, however, for the engines for applications such as pumps and decontamination units to be light weight and easily portable.
Attempts further have been made to develop igniters that can generate sufficiently high heats of combustion sufficient to ignite heavy fuels without requiring the high compression ratios and compression loads typically generated in conventional heavy fuel engines. For example, U.S. Pat. Nos. 4,977,873, 5,109,817, 5,297,518 and 5,421,299 disclose catalytic igniters having a catalyst material wound about an igniter rod which generally is heated to typically around 1200xc2x0 C. The problem with such igniters has been reliability as the igniter rods are subjected to vibration during engine operation and as current is passed through the catalyst wire wound thereabout, which has caused the rods to crack or break, causing failure of the igniter. In addition, it still has been necessary to significantly compress the diesel fuels to try to form vapors that can be readily ignited by the igniter.
Accordingly, it can be seen that a need exists for a low cost internal combustion engine capable of being operated using multiple different types of fuels including less volatile heavy fuels such as JP5, JP8, Jet A, diesel fuel and kerosene based fuels, which is able to ignite such heavy fuels at reduced compression ratios so as to enable the engine to be constructed of lighter weight components and be easily portable without a significant loss of power output by the engine.
Briefly described, the present invention comprises a multi-fuel engine for use with a variety of different types of fuels including gasoline and alcohol based fuels and heavy fuels including diesel fuel, JP5, JP8, Jet-A and kerosene, at relatively low compression ratios. As a result, the multi-fuel engine of the present invention can be built using smaller, lighter components for ease of portability and is useable with a variety of different types of fuels without a significant reduction in power output by the engine.
Typically, the multi-fuel engine of the present invention includes an engine block having a series of one of more cylinders and an engine air inlet and engine exhaust, a manifold or cylinder head mounted over the engine block, and a crankcase mounted to the lower end of the engine block. A crankshaft is extended through the crankcase, with the crankshaft being driven by the engine and being connected to an application such as a pump or drive.
In a first embodiment of the present invention, the engine block includes at least one cylinder defining a cylinder chamber having open upper and lower ends and which communicates with the engine air inlet and engine exhaust. A piston is received within and moves along the length of the cylinder chamber. The piston includes a piston body having a head portion and a skirt portion. A connecting rod connects to the body of the piston to the crankshaft such that as the piston is moved along the cylinder chamber, the reciprocating movement of the connecting rod with the piston drives the crankshaft of the engine.
The manifold or cylinder head is mounted over the engine block and defines a combustion chamber that is open to and communicates with the cylinder chamber of the engine block. The combustion chamber generally includes an upper, domed or semi-spherical portion and an open lower end that enables the passage of gases to the cylinder chamber. During operation of the engine, a combustible mixture of fuel and air is ignited within the combustion chamber, causing the piston to be driven along the cylinder of the engine.
A fuel delivery system is mounted to the manifold and includes a fuel metering device, for drawing in and mixing fuel and air for forming a combustible mixture of fuel and air that is ignited in the combustion chamber. The combustible mixture is drawn from the fuel metering device by a compression cylinder assembly and is compressed and directed through a fuel delivery valve. The compression cylinder assembly includes a cylinder chamber into which the combustible mixture is drawn, an auxiliary piston having a head portion, a skirt portion, and a connecting rod connected to an auxiliary crankshaft that is driven off of the rotation of the main crankshaft of the engine for driving the auxiliary piston. As the piston is moved along the cylinder chamber, the combustible mixture is compressed within the compression cylinder and is directed through the fuel delivery valve at a substantially sonic rate of flow and at a valve cracking or opening pressure sufficient to open the fuel delivery valve.
The fuel delivery valve is mounted within the manifold between the compression cylinder assembly and the domed upper end of the combustion chamber along a valve passage. The fuel delivery valve includes a valve body having upper and lower ends and defining an open ended channel extending therethrough. A valve member or poppet is received within the channel of the valve body and has an air/fuel passageway extending from an inlet opening in the upper end of the valve member to an intermediate point. The valve member also has an outwardly flaring lower end of the same approximate diameter as the inside diameter of the valve passage of the valve body so as to seal the open lower end of the valve body.
Recesses are formed in the valve body adjacent its upper end, in which a series of spring washers are received. The spring washers bias the valve member upwardly to a closed position, with the number and size of the springs setting the opening or cracking pressure required to open the valve. A retainer washer is received about the upper end of the valve member, above the spring washers, and acts as a stop to limit the size of the valve opening of the valve body. The retainer washer can be varied in size to vary the size of the valve opening created between the lower ends of the valve member and the valve body when the valve member is moved to an open position, to enable greater or lesser amounts of the combustible mixture to pass therethrough.
Typically, the opening pressure of the fuel delivery valve is set at one atmosphere or greater such that to open the fuel delivery valve, the combustible mixture is directed through the air/fuel passageway of the valve at a sonic velocity. As a result, the fuel within the combustible mixture including heavy fuels, is caused to be substantially atomized within the air, increasing the surface area of the fuel that is exposed to the air and enable the fuel to more readily form vapors for ignition.
The ignition system preferably includes a catalytic igniter having an igniter body generally formed from brass or steel with a first, nozzle end and a second, closed end in which a series of igniter ports are formed. An igniter rod generally formed from a dielectric material such as a ceramic material is received within the igniter body and includes a first, positive contact end and a second, negative contact end that is received at the second end of the igniter body within a seat formed at the second end of the igniter body. As a result, both ends of the igniter rod are supported within the igniter body.
A catalyst material such as a platinum wire or a tape having a platinum ink printed thereon is applied along the length of the igniter rod with areas of increased thickness of the catalyst material at each of the ends of the igniter rod. A heating zone is formed from a concentration of the catalyst material at an intermediate point along the igniter rod adjacent the second end. Electrical current is applied along the igniter rod through the catalyst material to the second end of the igniter rod engaged within the seat of the igniter body so that the igniter body acts as a ground. This causes the catalyst material to be heated at the heating zone to between approximately 900 to 1800xc2x0 C.
A portion of the combustible mixture delivered to the combustion chamber flows into the igniter through the igniter ports and comes into contact with the heating zone of the igniter, resulting in ignition of the combustion mixture. The ignition of the combustible mixture creates an explosion within the combustion chamber, causing the piston to be driven along the length of the cylinder chamber to drive the crankshaft. It also will be understood that conventional spark plugs can be used in place of the catalytic igniter.
An oil injection system is provided between the auxiliary crankcase of the compression cylinder assembly and the air intake for the primary or main cylinder of the engine. The oil injection system includes an oil injection line connected to the auxiliary crankcase and having a check valve and nozzle projecting into the engine air inlet. As the auxiliary piston is driven, oil and air are drawn into the compression cylinder crankcase from an oil pump to lubricate the compression cylinder assembly. This air and oil thereafter is urged along the oil injection line and into the engine air inlet passage, where it is drawn into the main cylinder crankcase with the inlet air for lubricating the main engine assembly.
An additional embodiment of the present invention comprises a three cylinder, two cycle engine having an engine block, crankcase and cylinder head. Each cylinder includes a main cylinder chamber, a stepped cylinder section, and an air intake through which ambient air is be drawn into the crankcase of the engine. A stepped piston is received within each cylinder and includes a head portion, a skirt portion and a step formed at the lower end of the skirt portion.
A stepped passage and an air injection passage are formed through the engine block adjacent each cylinder, extending in to the cylinder head or manifold. A secondary air intake communicates with the stepped passage such that as the stepped piston is moved along the stepped cylinder section, a negative air pressure is created so as to draw air into the stepped passage. Thereafter, as the stepped piston is moved along its upward stroke, the step of the piston urges the air from the stepped passage into and along the air injection passage to a fuel metering mechanism or device for mixing with fuel to form the combustible mixture. It is also possible to open the air injection passage to the crankcase to draw air from the crankcase into the air injection passage.
The fuel metering module and fuel delivery valve also can be mounted in a variety of positions about the combustion chamber and deliver the combustible mixture of fuel and air at a substantially sonic velocity so that the fuel droplets are substantially atomized within the air of the combustible mixture delivered into the combustion chamber and main chamber of each cylinder. A series of one or more igniters generally are mounted at the combustion chambers of the cylinders for igniting the combustible mixture.
Various objects, features and advantages of the present invention will become apparent to those skilled in the art upon reading the following detailed description, when taken in conjunction with the accompanying drawings.